The volatile organic component (VOC) as a percentage of printing inks is rapidly becoming an important environmental issue. Formulations in many ink types have traditionally consisted of relatively high molecular weight polymers, a mixture of additives, pigment, and one or more volatile hydrocarbon solvents. These solvents may represent a potential worker exposure hazard and are also known to contribute to the tropospheric air pollution problem as well.
In order to overcome the problems associated with using solvents, both in the ink industry and other coatings industries, new technologically advanced products have arrived on the market. Present technology includes the use of water borne, high solids, and powder coating systems. High solids products are based on the solventless system in which polymerization occurs after application of the coating or ink are also available. These products usually employ relatively low molecular weight, highly functional resins in conjunction with a cross-linking agent and a "reactive diluent", if necessary, for viscosity reduction.
Lithographic printing is a process which utilizes a coated metal or polymeric plate containing a hydrophobic image area which accepts, i.e., it is wetted by, hydrophobic based ink and a non-image hydrophilic area which accepts water, i.e., the fountain solution. As practiced in the prior art, high speed web presses use inks that contain organic solvents to transport the ink. The drying of the printed ink film is achieved by solvent volatilization at a substrate temperature of about 150.degree.-200.degree. C. Consequently, the use of such inks in the prior art requires highly sophisticated emission control equipment in order to comply with clean air and occupational standards for exposure to organic solvents. Considering these environmental standards and the costs associated with complying with them under practical industrial conditions, artisans in the field of ink development have been vigorously engaged in the development of new inks that will more readily meet environmental standards but still provide the quality performance demanded for the final printed product.
It is an objective of the present invention to provide a solvent-free, high solids, low VOC printing ink.
Another objective of the invention is to provide a solvent-free printing ink having a high level of flow properties, self structure capability and that is very fast drying.
Yet another objective of the invention is to provide the printing industry a solvent-free, fast drying, vegetable oil based "environmentally friendly" printing ink.
The foregoing objectives plus other features and advantages are achieved through the practice of the discoveries of the instant invention as described hereinafter.